1. Field of the Invention
The present invention relates to storage systems which include a storage controller for controlling storage devices such as a magnetic tape device, a semiconductor storage device or an optical disk device connected to a large-scale computer, a network system or the like. More particularly, the present invention relates to a storage system which is highly extendable and which allows degraded operation and hot replace.
2. Description of the Related Art
A conventional storage system connected to a large-scale computer is disclosed in, for example, JP-B-61-43742 (corresponding to U.S. Pat. No. 4,636,946). In the system disclosed therein, interfaces (host adaptors) with a higher-rank or host device (computer) (CPU), a cache memory, and interfaces (disk adaptors) with a storage device such as a magnetic disk device are interconnected by hot lines (dedicated lines).
FIG. 20 shows a schematic arrangement of a conventional storage system. In the drawing, reference numerals 201-1 to 201-n denote host adaptors connected respectively to a plurality of host computers (CPUs) (logical modules connected to a host computer), 202-1 to 2-2-n denote disk adaptors (logical modules connected to a storage device) connected to a shared large-scale disk device 205, 203 denotes a cache memory shared with the plurality of host adaptors, and 206 denotes a shared management memory. In a conventional storage system, hot lines 207-1 to 207-n and 208-1 to 208-n are connected between the host adaptors 201-1 to 201-n and cache memory 203, between the cache memory 203 and disk adaptors 202-1 to 202-n, between the host adaptors 201-1 to 201-n and management memory 206 and between the management memory 206 and disk adaptors 202-1 to 202-n respectively. Further, maintenance processors (SVPS, not shown), which carry out monitoring and maintenance operations over these host adaptors and disk adaptors, are connected to the respective host and disk adaptors through respective dedicated lines.
In the prior art system described above, since the hot lines are wired between the host adaptors (logical modules connected to the host device) to the host device, the disk adaptors (logical modules connected to the storage device) to the storage device, and the cache memory (cache memory module), the system configuration becomes more complicated, and the host adaptors, cache memory, disk adaptors and disk device are poorer in extendability, which makes it impossible to realize a so-called scalable (extendable and reducible) system configuration. Further, in prior art systems, no consideration is paid to the fact that multiplexing of the system enables degraded operation(one of the system multiplexers is stopped and the other alone is operated) at the time of failure occurrence or Hot replace (a substrate or a circuit part is inserted for its exchange while the system is being operated). For this reason, prior art systems such as the one described above have a problem in that, when it is desired to perform an exchange or replacement of parts at the time a system failure occurs or when it is time to up grade a system control program, the entry system must be temporarily stopped to perform that purpose.